(a) Technical Field
The present invention relates to a method and system for variably adjusting output voltage of a LDC for a hybrid vehicle, and more particularly, to a method and system for variably adjusting voltage of the LDC by applying an intelligent battery system (IBS) to the hybrid vehicle.
(b) Background Art
In general, a low voltage direct current-direct current (DC-DC) converter (LDC) is a device that switches direct current to be converted into alternating current (AC), increases or decreases the alternating current using coils, transformers, capacitors, etc., and rectifies the increased or decreased alternating current to be converted into the direct current again. The LDC installed within the hybrid vehicle is configured to convert high DC voltage from the high voltage battery to low DC voltage to charge an auxiliary battery, and monitor the amount of electric loads of the hybrid vehicle to supply electricity to suit voltage used in each electric load.
A voltage control method of the LDC in the related art is based on a driving mode of the hybrid vehicle and a temperature around the auxiliary battery without detecting a charged status of the auxiliary battery. Thus, the charge efficiency of the auxiliary battery decreases and a fuel efficiency effect may be difficult to improve. The voltage control method of the LDC in the related art will be described hereinafter.
FIG. 1 illustrates a voltage control flow of an LDC according to the related art. In voltage control of the LDC, a higher (e.g., an upper or dominate) controller, i.e., a hybrid control unit (HCU) transmits a voltage order to a lower controller (e.g., a subordinate), i.e., the LDC. In particular, the higher controller is configured to determine a control priority based on durability of the auxiliary battery and a degrading driving performance caused by use of high electric loads. Thereafter, when the voltage control of the LDC is normally accomplished, a LDC voltage control mode is determined based on various driving statuses such as a gear lever position, a fuel injection status, a vehicle speed, a motor torque, LDC power consumption, and so forth.
As listed in Table 1 below, the LDC voltage control mode is determined for each driving condition of maximum 7 driving conditions (e.g., a vehicle stop state, a deceleration period, an EV mode, an idle state, HEV mode, parking (P) stage, and a rear (R) driving state) based on the gear lever position, the fuel injection status, the vehicle speed, the motor torque, the LDC power consumption, and so forth.
TABLE 1Vehicle driving conditionVehicleMotorGearFuelspeed, 2 kphtorque, 5 NmPositionInjectionor moreor moreVehicle state—XX—Vehicle stop state—X◯XDecelerationperiod—X◯◯EV mode—◯X—Idle state—◯◯—HEV modeP———P stage parkingR———Rear driving state
Therefore, reference voltage order values which are mapped according to the LDC output voltage control modes determined for each of 7 driving modes is output from the LDC based on the temperature surrounding the auxiliary battery and the current power consumption amount of the LDC.
However, since the LDC output voltage control mode is subdivided into 7 driving modes, frequent changes of LDC output voltage order occur as the driving mode changes. As a result, the lifespan of the LDC may decrease and durability of the LDC may be degraded. In particular, during the LDC output voltage control mode, the LDC output voltage order may be alternately controlled to increase and decrease based on the change of the driving mode without detecting the charge status of the auxiliary battery, thus causing ineffective influence on the fuel efficiency such as increased consumed energy of the LDC.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may include information that does not form the related art that is already known in this country to a person of ordinary skill in the art.